Microcirculation in Renovascular Hypertension Renal artery stenosis (RAS) is becoming a more common etiology of end-stage renal disease. Despite the advances in renal revascularization techniques and stenting, the stenotic kidney often does not improve and even continues to deteriorate after a successful intervention, and the mechanisms leading to these grave outcomes have not been elucidated. We have shown that the kidney after 12 weeks of stenosis has marked microvascular loss and parenchymal damage, accompanied by decreased expression and availability of vascular endothelial growth factor (VEGF), a key physiological and pathological mediator of angiogenesis. Unlike acute ischemia, chronic reduction of renal blood flow (RBF) may fail to sustain VEGF production, which may thereby decrease renal microvascular density and perfusion in the stenotic kidney and lead to progressive and irreversible renal damage. Yet, the role that microvascular damage and loss has in deterioration of the stenotic kidney and the potential for improving the outcomes by protecting the renal microcirculation remain unknown. Importantly, our preliminary data show that RAS increases endothelin (ET)-1, a potent renal vasoconstrictor and down-regulator of the VEGF pathway through activation of the ET-A receptor. Thus, the overall hypothesis underlying this proposal is that RAS results in ET-1 mediated decreases in VEGF, leading to a decreased renal microvascular density, decreased renal function, and irreversible renal injury. Moreover, the current proposal will test the hypothesis that the hemodynamics and function of the stenotic kidney in response to revascularization (by percutaneous trasluminal renal angioplasty) will be improved by preserving the intrarenal microvasculature. We have developed a swine model of RAS that closely mimics the renal functional and structural changes that occur in humans with RAS, allowing us to use powerful physiological imaging techniques to characterize single-kidney function and structure. We have shown that fast computerized tomography (CT) characterizes non-invasively in vivo renal volume, perfusion, GFR, RBF and tubular dynamics, as well as endothelial and epithelial function, while micro-CT allows the 3D reconstruction of the renal microcirculation in situ. Thus, the function and structure of the swine RAS kidneys treated with ET-A receptor blockers or intra-renal VEGF, before and after revascularization, will be studied during the evolution of RAS. Relevance: The role and mechanisms of intra-renal microvascular injury in defining the progression of renal injury and the outcomes of the ischemic kidney after revascularization will be determined for the first time. We will also determine the mechanisms associated with irreversible renal injury, and the timeframe during which the function of the ischemic kidney could be preserved or restored after established renal injury. These studies will advance our understanding of the pathogenesis of renal ischemia, will identify injury markers and predictors of renal viability, and provide viable treatment options for patients with renovascular disease.